This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-199397 filed on Jun. 29, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a detector for detecting a deceleration impact exceeding a predetermined level caused by an accidental collision or the like. The detector is used, for example, to generate a signal for inflating an air-bag mounted on an automotive vehicle.
2. Description of Related Art
A conventional collision detector is disclosed, for example, in JP-A-2000-182488. The collision detector disclosed in this publication, as shown in FIG. 10, is composed of a rotor 110 rotatably supported by a rotor shaft 100, a cam 120 fixed to the rotor 110, a pair of contact springs 130, 140 which are closed by the cam 120 when the rotor 110 rotates by a predetermined rotational angle, and a printed circuit board 150 having an electrical circuit for generating a signal upon closing of the pair of contact springs 130, 140.
Referring to FIGS. 11 and 12, operation of this collision detector will be explained. When a deceleration is caused by a vehicle collision, the rotor 110 rotates in a direction shown by xe2x80x9cbxe2x80x9d against a biasing force Tset (in a direction shown by xe2x80x9caxe2x80x9d) of a contact spring 130. The contact spring 130 is pushed by the cam 120 rotating together with the rotor 110 and is resiliently deformed thereby to contact the other contact spring 140. Upon closing of the contact springs 130, 140, an electrical signal (an ON signal) for inflating an air-bag is generated.
However, there are following problems in this collision detector. (1) After the contact spring 130 contacts the other contact spring 140, the other contact spring 140 resonantly vibrates due to a collision impact, and thereby a contact between two contact springs 130, 140 cannot be maintained. Accordingly, a stable and reliable signal is not obtained form the collision detector. (2) Since the contact spring 130 biases the rotor 110 toward its initial position, an abrasion torque is always applied to the rotor 110. A dispersion of the abrasion torque causes a functional dispersion of the collision detector. (3) The contact spring 130 contacts the other contact spring 140 at a rotational angle, i.e., at an ON position shown in FIG. 12. Since after the ON position, the resilient force of the contact spring 140 is additionally applied to the rotor 110, a value Tset/MR (Tset is a biasing force in the direction xe2x80x9caxe2x80x9d and MR is a rotational moment of the rotor in a direction xe2x80x9cbxe2x80x9d) rapidly increases. Therefore, it is difficult to maintain the ON signal for a long time. (4) Since a housing base 170 is connected to a housing 160 supporting the rotor shaft 100, as shown in FIG. 11, a dimensional dispersion in connecting the housing base 170 to the housing 160 causes a dispersion in function of the collision detector. (5) A rotor assembly mounted on the housing 160 is inserted into an inside space of a casing 180, and a gap between the housing 160 and the casing 180 has to be sealed. If a sealing material is supplied into the gap, it leaks into the casing 180. Therefore, instead of using the sealing material, a packing 190 covering the bottom end of the casing 180 is disposed to provide a hermetical sealing, as shown in FIG. 10. Further, a lid 200 covering the packing 190 is connected to the bottom end of the casing 180 by heat-staking the bottom end. Use of the packing 190 and performing the heat-staking require an additional manufacturing cost.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an improved deceleration impact detector which functions with a high stability and reliability and can be manufactured at a low cost.
The deceleration impact detector is used for detecting a high deceleration generated by an accidental collision of a vehicle or the like. An air-bag for protecting a passenger is inflated upon receipt of an electrical signal from the deceleration impact detector. The deceleration impact detector includes a rotor having its gravity center eccentric relative to a rotational center of the rotor, a coil spring biasing the rotor to its initial position, a cam connected to the rotor, and a contact member consisting of a resiliently movable contact and a stationary contact. When a deceleration exceeding a predetermined level is imposed on the rotor, the rotor rotates so that the cam connected to the rotor pushes the movable contact thereby to close the contact member. Upon closing the contact member, the detector generates an ON signal for operating the air-bag.
The movable contact is made of a resilient leaf spring and the stationary contact is made of a plate having a high rigidity, thereby to avoid resonant vibrations of the stationary contact upon receipt of a high deceleration impact. The movable contact is positioned apart from the cam, forming a certain space therebetween, when the rotor is at its initial position. In this manner, rotation of the rotor is not restricted by the resilient force of the movable contact.
The cam includes a first surface for pushing the movable contact and a second surface continuing from the first surface. The second cam surface is formed in a circular curvature around the rotational center of the rotor, so that the movable contact is not further pushed according to the rotation of the rotor after the contact member is closed. The electrical ON signal is maintained by the second cam surface while avoiding the resilient force of the movable contact from being applied to the rotor.
Components of the detector including the rotor, the coil spring and the contact member are mounted on a housing having a rectangular housing base. The rectangular housing base is press-fitted into a rectangular opening of a casing thereby to contain the housing in the casing. Flanges extending from the four corners of the housing base are formed, so that the flanges are tightly received on receiving surfaces formed at corners of the casing. The housing base and the casing are hermetically sealed with a filler material filling small spaces between the housing base and the casing. The housing base may be separated into two parts, a base frame and a base plate press-fitted into the base frame, both parts being connected by crank-shaped connecting pins formed by molding.
According to the present invention, the deceleration impact detector stably functioning with a high reliability and having a simple structure is manufactured at a low cost.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.